Computed tomography (CT) is a widespread diagnostic imaging method which measures the x-ray attenuation coefficient of matter. This x-ray attenuation coefficient is depicted in terms of Hounsefield Units. During a CT scan, a collimated X-ray beam is directed on the patient and the attenuated remnant radiation is measured by a detector whose response is transmitted to a computer. The computer considers the location of the patient and the spatial relationship of the x-ray beam to the region of interest and analyzes the signal from the detector so that a visual image of the region of interest can be reconstructed and displayed on a monitor. The image can then be viewed or stored for later evaluation.
Hounsefields Units reflect the relative absorption of the CT x-rays by matter, where the absorption is related to the atomic number, electron density, physical thickness of the matter, and the energy spectrum of the x-rays. Because of the similarity in electron density of various tissues in the body, CT scans sometimes result in poor imaging. In an attempt to obtain better results in such circumstances, a contrast agent, such as iodine, can be injected in the patent's blood stream to change the relative radio-density of the tissues, and improve the overall diagnostic capabilities of the procedure.
In addition to CT, magnetic resonance imaging (MRI) is a clinically important medical imaging modality because of its exceptional soft-tissue contrast. MRI exploits the existence of induced nuclear magnetism in the patient body. The magnetic resonance signals from water and the hydrogen atoms in fat are mapped according to their location within the patient so that the internal organs of a patient can be imaged without the use of ionizing radiation. Since its development nearly 30 years ago, MRI has become an invaluable medical imaging modality. Just like CT, contrast enhancement is extremely valuable in MRI for the visualization of normal tissue as well as the diagnosis of soft tissue diseases. Although there is an intrinsic contrast between a lesion and surrounding tissue in MRI, it is critical to selectively enhance the pathology or the structure of interest by administering a contrast agent. The most common agent used in MRI is Gadolinium, which can dramatically improve the conspicuity of the lesion and the image quality, particularly in magnetic resonance angiography.
The volume of Gadolinium used in a typical MRI procedure is usually around 20 cc, which is one-fifth of the amount of iodonated contrast used in a typical CT procedure. Because of this small volume, the relative amount of Gadolinium remaining in an injection tubing after completion of the injection is substantial. To prevent waste, it is important to completely inject any Gadolinium remaining in the tubing at the completion of injection.
Contast agents may be administered either manually through hand injection of a syringe or automatically through the use of power injection equipment. Several manufacturers, including Mallinckrodt Medical Inc. and MedRad Inc., produce a wide variety of power injectors for use in both CT and MR procedures. These power injectors may be either a single barrel style for injection of one syringe as in most of CT injectors or double barrel style for injection of two syringes as in most of MRI injectors, although the single barrel style tends to be more commonly used.
Contrast agents are typically provided in a bottle and are drawn into a syringe immediately prior to use in either manual or power injection imaging procedures. In applications where a relatively small volume of contrast agent is used, such as in an MR imaging procedure using Gadolinium, injection of the contrast agent may be performed by manual injection with a common syringe with injection tubing and an angiocatheter placed in the arm. In other applications, the syringe may be manually prepared for use in a power injector. As with any manual procedure, manual preparation of syringes involves multiple steps that are time-consuming and associated with potential contamination problems and dosing errors.
To alleviate the problems inherent in manually preparing syringes of contrast agent, some suppliers provide contrast agents in prefilled syringes that can be used in either manual or power injection procedures. The prefilled syringe is gaining wide acceptance because it can reduce the complications and the number of steps previously associated with using bottled contrast agents, and a recent survey by the American Society of Radiologic Technologists reported that using a prefilled syringe in power injection equipment resulted in improved efficiency and quality of service, and less wasted contrast agent.
In CT and MR imaging procedures, the injection of a contrast agents maybe followed by the injection of a saline solution, which is commonly referred to as a saline flush or saline chase. The saline injection has several advantages in that it reduces the amount of contrast agent used and prevents waste. Previously, when planning an imaging procedure, the amount of contrast agent to be injected had to be increased to compensate for the amount of contrast agent left in the injection tubing at the completion of the procedure between the syringe and the patient vascular access injection site. Ordinarily, this amount of contrast agent is discarded along with the injection tubing at the end of the procedure. However, by using the saline flush, almost all of the contrast agent in the syringe can be used because the contrast agent that remains in the injection tubing between the injector and the patient vascular access injection site is injected into the body with the saline flush. The saline flush is also beneficial because it provides a final push and continuous steady flow of the contrast agent that is slowly flowing in the peripheral blood stream at the tail end of the injection, thereby improving efficient use and diagnostic contribution of the contrast agent that is already injected into the body. The saline flush also disperses the contrast agent accrued in the central venous structures at the tail end of the injection to reduce associated artifact at the injection site. Finally, injecting 10-20 cc saline after the completion of a contrast CT study is a standard practice to clear up any residual contrast agent which may clog the vascular access site because of its high viscosity.
Despite its known benefits, the injection of a saline bolus immediately following the contrast agent is not commonly practiced. Most often, the saline flush injection is administered by using a double barrel power injector that can inject two syringes independently and sequentially. In the double barrel injector, one of the injector barrels is used for injecting the contrast agent and the other injector barrel is used for injecting the saline flush solution. In a double barrel power injector set-up, each of the syringes in the injector has a tubing that leads from the syringe to a one-way valve and then to a Y-adapter which then leads to a common injection catheter. The double barrel power injector allows for a precise amount of contrast agent to be injected from the first syringe at a steady and continuous injection rate followed immediately by the injection of saline from the other syringe. Without a double-barrel injector, injection may be performed manually, but a manual injection cannot provide the precise injection rate required to produce good-quality images, particularly when CT contrast agent is injected, which tends to be very viscous. Additionally, with manual injection, it is often difficult to inject the saline flush rapidly and immediately after injection of the contrast agent without any gaps in the bolus. Because most CT power injectors are of the single barrel style, a saline flush is typically not performed. Thus, to provide the benefits of the saline injection after the injection of the contrast agent, what is needed is a single pre-filled syringe that stores both substances separately and can inject them sequentially either manually or through existing single barrel power injection equipment.
In the medical field, a dual chamber prefilled syringe has been commonly used to separately store two substances, usually a medical component and a vehicle. However, these syringes do not allow for sequential injection of the substance, but are intended to provide a thorough mixing of the substances into a homogeneous injection liquid before injection. In the syringes described in U.S. Pat. Nos. 5,788,670 and 5,865,799, the two substances are mixed within the prefilled syringe and then directly injected from the prefilled syringe. Typically, the dual chamber prefilled syringe is formed of a single syringe barrel made of glass or plastic with an end plunger and rod positioned opposite of the syringe head. An intermediate plunger is positioned in the barrel of the syringe to divide the barrel of the syringe and create two separate chambers in the syringe for separately storing the substances before injection. When injecting the contents of the syringe, the plunger rod connected to the plunger is moved forward in the direction of the syringe head thereby forcing the intermediate plunger through the syringe until it reaches a bypass positioned in the mid section of the syringe barrel, which allows the substance in the second chamber to flow into the first chamber where the two components are then subsequently mixed and injected by the continued movement of the plunger and plunger rod. While conventional syringes of this type are effective for mixing two substances immediately before injection to reduce the risk of cross contamination and to allow effective packaging of the substances, conventional syringes of this type do not allow for sequential injection of the components in the syringe so as to allow their use in an imaging application with saline flush as described above.
What is needed is a syringe capable of sequentially injecting two substances from one syringe. Such a syringe would be readily useable in imaging applications as the syringe would be preferably pre-filled with a desired contrast agent and a saline solution to provide in-line flushing in the injection tubing to prevent waste of the contrast agent even when small volumes of contrast agent are used. Such a syringe would be readily adaptable to fit in existing power injection equipment such as the commonly used single barrel injector described previously or a double barrel injector where only one side of the injector need be used. By providing the flush solution in line with the contrast agent, all of the contrast agent in the tube can be used instead of discarding the residual contrast agent that is ordinarily left over in the injection tubing in the double barrel injector between the syringe head and the “Y” connector or in the single barrel injector between the syringe head and the patient injection site. Such a syringe would allow the use of a saline flush with the single barrel injector to achieve the clinical benefits described above that are ordinarily only achieved through the use of the less common double barrel injector.